This invention relates to antenna mounts and more particularly to tracking antenna mounts capable of providing angular motion for an antenna structure.
Tracking antenna mounts in general provide for angular motion of an antenna structure (dish, horn, lens phased arrays, etc.), such that the antenna can receive or transmit signals in a continuously selectable direction with respect to the base structure to which the antenna mount is secured.
Most existing tracking antenna mounts are gimbaled structures such that successive gimbals are rotated by some angle with respect to the adjacent gimbal. A tracking antenna mount is characterized by the number of such rotations, and is usually either 2-axis or 3-axis.
2-AXIS ANTENNA MOUNTS IN GENERAL USAGE ARE: (1) AZ-EL, where the outer axis is the azimuth axis and is in a vertical direction with respect to the base structure and the inner axis is the elevation axis and is in a horizontal plane; (2) X-Y, where the outer axis is the X-axis and is in a fixed horizontal direction with respect to the base structure and the inner axis is the Y-axis and is in a plane normal to the X-axis; and (3) HA-DECL, where the outer axis is the hour angle axis and is parallel to the Earth's polar axis and the inner axis is the declination axis and is in the equatorial plane.
All of the 2-axis mounts enumerated above have a pole or discontinuity in the direction of the outer axis. Severe limitations on tracking (motion of the antenna axis) exist in the vicinity of the pole.
3-AXIS ANTENNA MOUNTS IN GENERAL USAGE ARE: (1) Traverse/Elevation/Azimuth; and (2) Elevation/Cross-Level/Azimuth. 3-axis antenna mounts avoid the difficulties around the pole which are experienced in 2-axis antenna mounts.
Another class of antenna mounts is the non-gimbaled variety, which may utilize linear actuators, ball joints, etc.
The disadvantages of the above-mentioned antenna mounts is that the 2-axis gimbaled antenna mount must always restrict or exclude operation near the pole or discontinuity direction. The 3-axis gimbaled antenna mount does not have a pole, but is more complex, and consequently more expensive and less reliable than the 2-axis antenna mount. Also, for the 3-axis gimbaled antenna mount the tracking control circuitry becomes more complex because of the redundant third axis. Existing non-gimbaled antenna mounts generally operate over a restricted coverage angle which is considerably less than a hemisphere.